1. Field of the Invention
The present invention relates to a method for forming an adhesive layer suitable for forming the adhesive layer on a semiconductor element and to an adhesive composition to be used for the forming method.
2. Description of the Related Art
The formation of an adhesive layer on a surface to be adhered is conducted by forming an adhesive composition on the surface while the coating method of the adhesive composition is appropriately selected based on the kind of material, configuration of the surface and the kind of adhesive agent.
Recently, digital equipments and mobile devices using respective semiconductor elements are remarkably developed in function, downsizing and weight saving. The downsizing and weight saving of a semiconductor product to be used require the thinning of the semiconductor element to be packaged in addition to the thinning of the corresponding semiconductor package. As of now, the thinning of the semiconductor element is conducted by grinding the corresponding semiconductor wafer at the pre-step prior to cutting the semiconductor wafer into the corresponding semiconductor elements through dicing so as to satisfy the extreme thin element thickness of 100 μm or less, particularly several ten vim or less. Therefore, the thickness of the adhesive layer for adhering the semiconductor element to a conventional metallic frame or organic substrate affects remarkably on the thinning of the semiconductor product.
In the case of the formation of a liquid adhesive agent, conventionally, the coating of the adhesive agent is conducted by means of dispensing or stamping.
With the recent development in sophistication of the digital equipments, however, there are some technical problems in the aforementioned coating method of the adhesive composition when the packaging method where a plurality of semiconductor elements with the respective different functions are stacked or the multi layered stacking method for enhancing a memory capacitance is employed.
Namely, in the stacking structure and multi-stacking process of thin semiconductor elements, since each of the thin semiconductor elements is warped due to the thin thickness thereof, some voids are created at the adhesive layer interface or in the adhesive layer due to the incorporation of air in the adhering process of the semiconductor elements or the thermal compression bonding process of the semiconductor elements with adhesive agents thereon, resulting in the deterioration of production yield (refer to, e.g., References 1 and 2)
Fundamentally, in the dispensing method and stamping method, it is difficult to form the adhesive layer in a thickness of several μm so as to be extremely thinned and a coating amount is likely to be fluctuated, resulting in the technical difficulty of the uniform and stable formation of the adhesive layer.
In order to iron out these problems, a filmy adhesive sheet is developed and attributes largely to flash memories of which the capacities are being increased by means of multilayered process. The use of the filmy adhesive sheet cannot only control the thickness of the adhesive layer uniformly at the step of the film formation, but also form a restively thin adhesive layer. However, it is difficult to make the filmy adhesive sheet uniform in a thinner thickness of several μm so as to be used in the aforementioned extremely thinner elements and the handling of the filmy adhesive sheet of a thickness of several μm is not good and practical in the case of direct adhesion thereof on a silicon wafer or a semiconductor element. Moreover, there are various problems to be solved as the manufacture of such an extreme thinner filmy adhesive sheet requires much cost in comparison with a conventional one.
On the other hand, in the functional complex due to the stacking structure of a plurality of semiconductor elements and the large capacity due to the multilayered structure of a plurality of semiconductor elements in order to realize the multifunction of the semiconductor product, the adhesive technique for the semiconductor elements becomes important. In the adhering step of the semiconductor elements, the precision of adhering position is very important for the wire-bonding step and the flip-chip packaging step after the adhering step.
It is considered that the precision of adhering position is most subject to the precision of coating position of an adhesive agent to be coated. Inherently, it is required that the adhesive agent is coated highly precisely onto the adhering position as designed. As the coating method of the adhesive agent onto a lead frame, an organic substrate or a semiconductor element as a base to be coated can be considered a screen printing method. In this case, it is difficult to coat the adhesive agent so as to form the adhesive layer in a thickness of several μm or so and in the handling of the adhesive layer forming step, since some components such as a screen mesh or a squeegee are contacted with the forming surface of the adhesive layer, there is a problem that the substrate may be destroyed when the substrate is a thin silicon wafer, a chipped semiconductor element or the like.
[Reference 1] JP-A 2008-270282 (KOKAI)
[Reference 2] JP-A 2008-288571 (KOKAI)